Helicopter rotor construction and improved rotor blade therefor having a retractible trailing portion



June 21, 1966 KLAUS-UWE EXNER 3,256,938

HELICOPTER ROTOR CONSTRUCTION AND IMPROVED ROTOR BLADE THEREFOR HAVING A RECTRACTIBLE TRAILING PORTION Filed April 13, 1965 4 Sheets-Sheet l lnl/enzor: Klaus Uwe Exner By MM m W Attorneys June 21, 1966 usw EXNER 3,256,938

HELICOPTER ROTOR CONSTRUCTION AND IMPROVED ROTOR BLADE THEREFOR HAVING A RECTRACTIBLE TRAILING PORTION Filed April 13, 1965 4 Sheets-Sheet 2 lnvemon Klaus-Uwe Exner By mw W Attornevs June 21, 1966 KLAUS-UWE EXNER 3,256,938

HELICOPTER ROTOR CONSTRUCTION AND IMPROVED ROTOR BLADE THEREFOR HAVING A RECTRACTIBLE TRAILING PORTION Filed April 15, 1965 4 Sheets-Sheet 5 lnvenzon' Klaus-Uwe Exner By MWWM Atfornevs June 21, 1966 KLAUS-UWE EXNER HELICOPTER ROTOR CONSTRUCTION AND IMPROVED ROTOR BLADE THEREFOR HAVING A RECTRACTIBLE TRAILING PORTION Filed April 13, 1965 4 Sheets-Sheet 4 lnvenzor:

Klaus-Uwe Exner MMMZM Attorneys United States Patent 20 Claims. (Cl .170-160.12)

This invention relates in general to helicopter rotor construction and to improved rotor blade constructions for such rotors and, in particular, to a new and useful helicopter having blades comprising a spar forming a forward portion of the blade air foil section and with a trailing or rear portion which is adjustable in respect to the forward portion for extending outwardly from the forward portion to provide full lift when the rotor is rotated and being inwardly collapsible toward the spar for terminating the lift characteristic such as when the rotor is stopped after vertical flight has been accomplished and additional power plant means are employed on the craft for forward flight.

The present invention is particularly directed to blade constructions for use in aircraft of a type which are referred to as convertible rotating wing aircraft. The present invention is an improvement over the prior art, particularly in respect to the provision of a blade structure including a rigid or semi-rigid spar element which forms the forward portion of the blade structure and is of a cross section providing for relatively low air resistance by itself. The blade structure further includes a trailing section which may be extended behind the spar for forming a full lift profile blade structure. A feature of the inventive construction is that the trailing section is collapsible relative to the spar and in a preferred arrangement, may be folded inwardly behind the spar when it is desired to materially reduce the air lifting characteristics of the rotor blade.

The present invention provides a rotor which is distinct from convertible rotary wing aircraft wherein the blade elements are folded backwardly into close proximity to the fuselage, or into cavities which may be defined thereon for accommodating such blades, when it is intended to shift from vertical flight to horizontal flight. Rotors of this type are relatively expensive and are therefore only justifiable in some cases, for example, in large convertible airplanes.

An object of the present invention is to provide a convertible rotary wing aircraft which includes rotor blade elements having a forward spar section and a trailing section which is foldable inwardly in respect to the spar for reducing the lift characteristics of the blade. In a preferred arrangement, the rear structure includes rigid structural units or ribs which are pivotal in respect to a forward spar portion and a trailing bar member or flap element forming the rear of the blade profile. The rib structure is advantageously pivoted bothto the forward spar and to the trailing flap element and all of the ribs may be collapsed toward the spar for the purpose of reducing the overall air foil section and hence the lift of the rotor blade. With such a construction, the rotor may be stopped and the level flight motors may be switched on for proceeding in horizontal flight. The construction is advantageous in that the rotor blades may be de-profiled at once over their entire length by holding the trailing section of the blade elements toward the forward section which forms the spar. By providing a trailing flap element which is connected to each of the rib structures along the length of the blade, it is a simple matter to collapse Patented June 21, 1966 the entire trailing section of the blade by displacing the trailing flap portion relative to the spar.

In accordance with a further feature of the invention, the trailing portion of the blade structure is made up of rib elements which may be pivoted in respect to the forward spar portion for folding purposes. In addition,

means are provided for causing the collapsing of the rib structures, that is, the inward movement of two rib parts so that they will be folded inwardly behind the forward spar portion without extending outwardly beyond the surface thereof and causing any drag or wind resistance. The inward folding of the forward portion of the rib parts is accomplished in accordance with the invention by means of wedge-shaped formations on the rib structures and the spar which cause the inward movement of the rib parts when they are folded.

A further feature of the invention is the provision of improved mechanism connected to the foldable trailing portion of each blade element so that the trailing portion may be folded inwardly toward the spar by means actuated from the inner end of the affected blade in a simple manner.

A further object of the invention is to provide a blade structure for a rotary wing aircraft which includes a rigid forward spar element forming the forward portion of the blade structural profile and a trailing section articulated in respect to the forward section, with means for collapsing the trailing section in a direction toward the forward section for de-activating the blade elements and for reducing the lift characteristics without materially increasing the drag.

A further object of the invention is to provide a blade structure for a rotary Wing aircraft which includes a forward air foil section spar element having a relatively low drag resistance with a trailing section made up of individual rib elements pivoted at spaced locations along the length of the forward section and, also pivoted to a trailing flap element and with an outer'covering or skin extending between the flap element and the forward spar element, and wherein the ribs are pivotally connected-at respective ends to said forward spar element and said flap element for the purposes of collapsing said ribs by moving the trailing flap element inwardly toward said forward spar element.

A further object of the invention is to provide a blade structure which is simple in design rugged in construction and economical to manufacture.

The various features of novelty which characterize the invention are pointed out with particularity in the claims annexed to and forming a part of this specification. For a better understanding of the invention, its operating advantages and specific objects attained by its use, reference should be had to the accompanying drawings and descriptive matters in which there are illustrated and described preferred embodiments of the invention.

In the drawings:

FIG. 1 is a partial perspective view of a rotor constructed in accordance with the invention with the rotor blades indicated with the rear structure in a fully extended position;

FIG. 2 is a view similar to FIG. 1, but with the rear structure indicated folded toward the forward spar structure;

FIG. 3 is a transverse section through a blade of the rotor indicated in FIG. 1;

FIG. 4 is a partial section taken on the line 44 of FIG. 3;

FIG. 5 is a section similar to FIG. 3, but with the trailing structure folded inwardly toward the forward spar structure;

FIG. 6 is a section similar to FIG. 4 indicating the parts with the rear blade structure folded inwardly;

FIG. 7 is a partial top plan view of a rotor blade having means for collapsing a trailing portion of the blade structure;

FIG. 8 is a view similar to FIG. 7 with the blade structure indicated in a collapsed condition;

FIG. 9 is a view similar to FIG. 7 of another embodiment of the invention;

FIG. 10 is a view of the structure indicated in FIG. 9 with the trailing structure of the blade folded inwardly;

FIG. 11 is a fragmentary perspective view of a rotor having means for collapsing each blade structure;

FIG. 12 is a partial elevational and partial sectional view of a rotor having a blade with means for collapsing the trailing structure thereof; and

FIG. 13 is a view taken on the lines 1313 of FIG. 12.

Referring to the drawings in particular, the invention embodied therein comprises a rotor for a convertible aircraft which includes a rotor head 1 which is rotatable about an axis parallel to the rotor shaft 2 and which carries blade elements or blades 50 which in the embodiment illustrated are connected to the rotor head through an extension of a forward blade portion or spar 3. The spar 3 forms the forward or nose portion of the blade profile structure and, in accordance with the invention, a trailing portion or rear blade structure 4 is collapsible inwardly toward the spar 3 When the rotor is to be deactivated or stopped. The rear blade structure 4 is connected to a connecting rod a which is slidable in a fluid cylinder 5 in accordance with the admission of a control fluid therein through lines (not shown). The outer that the pivot points are offset from the longitudinal center line of the ribs, there is a point of maximum spacing between the nose spar 3 and the trailing flap 8 which is passed during the extension of the rear structure 4 and end of the rod 5a is connected to the rear blade structure 4 and when the rod 5a is moved outwardly in the cylinder 5 it causes the rear blade structure 4 to move longitudinally and inwardly in respect to the spar 3. In the collapsed position indicated in FIG. 2, the lift characteristics of the rotor is eliminated completely or substantially completely even though the rotor blades will maintain their moment of inertia unchanged.

As best indicated in FIGS. 3-6 the rear blade structure 4 includes ribs generally designated 7 which extend in transverse directions as indicated in FIGS. 3 and 4 when the rotor is being rotated to produce a lift, but which are folded to extend substantially longitudinally in respect to the blade, that is, radially outwardly from the hub to the positions indicated in FIGS. 5 and 6 when the rotor is to be stopped. A plurality of ribs 7 are provided at spaced locations along the spar 3 and each rib comprises leg portions 20, 20 interconnected at the trailing end by a web portion 20a. The ribs are connected to a trailing flap element or connecting bar 8 through a pin 10 about which they are pivotal. Each rib element 7 includes an offset portion 20b at one end and an oppositely offset portion 20c at an opposite end. The offset portion 200 is connected to the spar 3 through a pivot pin 17 and each leg portion 20, 20 includes such an offset portion.

In addition to the ribs 7 and the trailing flap 8, the rear blade structure 4 includes an outer skin or covering of flexible material 9. The covering 9 is advantageously secured to the spar 3 and to the trailing flap 8 and is elastically deformable.

According to a feature of the construction, the offset ends 20b and 200 of the ribs 7 insure that the ribs 7 will extend at substantially right anges to the longitudinal axis of the blade. The pivot locations defined by the pins 10 and 17 are arranged at spaced locations from opposite sides of the longitudinal center line of the ribs in order to facilitate the in-folding of the ribs when the rotor is to be stopped. The wide edges produced by the offset portions 20b and 200 provide a firm support in an extended position as indicated in FIG. 4 against the respective spar 3 and trailing flap 8. Because of the fact before the end position is reached. The ribs 7 are thus secured in their final position by the tension of the pro file skin 9 independent of the nature of the shifting mecha- According to another feature of the invention, the trailing flap 8 is constructed so that its outer edge 12 forms the trailing edge of the blade profile. In this manner, the construction of the ribs may be made considerably simpler and the connecting bar may function as a means for shifting the rear structure inwardly in a simple manner.

The skin or covering 9 is secured on the nose spar 3 and recesses 13, and also is secured to the rear edge of the flap 8, for example, such as by cement or in any other known suitable manner. The skin or covering 9 can also be secured on the ribs 7 in those instances where it is found expedient to do so, but this would vary from situation to situation. When the rear structure 4 is extended, the covering 9 is stretched over the ribs 7. When the rear structure 4 is folded downwardly, the profile skin or covering 9 is folded in the longitudinal direction of the blade behind the nose spar 3. The folds 14, indicated in FIG. 5, will be under stress parallel to the axis of the nose spar 3 due to the displacement of the rear edge 12 of the rear structure 4 so that .the folded portions will not flutter. The entire rear structure 4 thus is maintained behind the spar 3 when the rotor is stopped and the configuration of such structure in the folded position is such that it will provide very low drag resistance.

In order to insure that the rear structure 4 does not protrude beyond the profile of the spar 3 in the folded state, the ribs 7 are advantageously made so that the forward edges at least may be compressed inwardly when they are collapsed against the spar 3. For this purpose, the trailing edge of the nose spar 3 is formed with a recess 15 having wedge-shaped or oblique flanks 16 which are bevelled from the outer ends of the spar inwardly toward the center. The forward ends of the ribs 7 are provided with similar wedge-shaped configurations and advantageously carry rollers 19 so that the wedge-shaped portions 18 roll over the wedge-shaped portions 16. When the ribs 7 are collapsed against the spar 3, the wedge-shaped portions 18 and 16 cooperate to cause an inward movement of the rib legs 20, 20. When the ribs 7 are folded outwardly away from the spar 3, a spring 21 provides means for biasing the leg portions 20, 20 away from each other so that they will bear against the outer skin 9 to hold it in a stretched condition in the fully erected condition. The ribs 7, of course, may be made of a rigid material instead of being adjustable in height as outlined, but this will be at the expense of an increase in harmful drag at the rear of the blade structure when it is folded down.

The rotor blade is designed so that the profile structure can be extended by centrifugal force of the rotor and folded down on the rear edge by tension. But the opposite case is also possible, namely that the profile structure can be extended by tension on the rear edge and folded down by the action of centrifugal force. In view of the requirement that the profile structure of the rotor blades must maintain their respective positions for the operation of the rotor in the extended and the folded state both with and without centrifugal force, it is preferable, according to the invention, that the shifting of the profile structure be effected by a crank which can-retain the profile structure in its two end positions.

In the embodiments of FIGS. 7 and 8 a crank drive 22 is provided for effecting the shifting from a folded-out to fining the folded-out position and another stop 26 defining the folded-in position of the rear blade structure. The crank 27 is connected through a link 22a to the trailing flap 8'.

In the embodiments of FIGS. 9 and 10, a three-armed lever 29 is provided for effecting the shifting from a folded-out to a folded-in position of the rear blade structure 4. The three-armed lever includes one arm portion 29a which is pivotally connected at 32 to the spar 3", another arm portion 29b which is connected to a control rod 31 which is actuated through a fluid control cylinder 28 and a third arm portion 29c which is connected through a link 33 to the trailing flap 8". The three-armed lever 29 is pivotal about the pivot point 32 from the out-folded position indicated in FIG. 9 to the in-folded position indicated in FIG. by directing control fluid through either conduits 52 or 54 in accordance with which direction the movement is to take place.

In FIG. 11, there is indicated another embodiment in which a disc or plate 36 is mounted concentrically on the rotor head over the rotor shaft 2. The disc or plate 36 includes equally spaced leg portions upon which are pivotally mounted connecting rod elements 37 for each blade structure. The plate 36 is rotated by means of a spirally grooved spindle 38 which may be moved in the direction of the arrow indicated to cause clockwise rotation or in an opposite direction to cause counterclockwise rotation as desired. Such movement causes a corresponding displacement of each of the trailing flaps 8 which are pivotally connected to the rod elements 37 (connection not shown).

In the embodiment indicated in FIGS. 12 and 13, there is indicated a device which will provide for the in-folding and out-folding of the rear structure 4 of each blade with- I out introducing any errors as a result of a blade angle control. Each blade is mounted on a pivot pin 41 on the rotor head 1 which, in the embodiment illustrated, is hollow. A reciprocable member 42 is slidable in the pivot pin 41 and includes a ball-shaped end 43 which engages an arcuate link 44 carried at the end of a tipping lever 45. The center of the arcuate link 44 lies in the blade angle axis. The tipping levers 45 are bent off in a right angle. They are pivotally mounted on an abutment 46 about the axles 47. On their free lever arm 48, the tipping levers 45 are so joined with the connecting bars 8 that they transmit the ascending and descending movement of the push rods 42 as a reciprocating movement. Suitable means (not shown) are connected to the push rods 42 for reciprocating them.

While specific embodiments of the invention have been shown and described in detail to illustrate the application of the inventive principles, it will be understood that the invention may be embodied otherwise without departing from such principles.

What is claimed is:

1. A blade structure for a rotary wing aircraft comprising a spar forming the forward portion of said blade structure and a collapsible rear blade structure connected to said spar and spaced rearwardly therefrom to form the rearward portion of said blade structure when in an extended position, said rear blade structure being connected to said spar in a manner permitting said rear blade structure to be collapsed inwardly toward said spar to present an overall profile together with said spar of relatively low said drag and with substantially no lift capabilities, a skin connected between said space and said rear blade structure and forming an exterior covering therebetween and providing therewith a lift profile when in an extended position and being folded between said spar and said rear blade structure in a collapsed position.

2. A blade structure for a rotary wing aircraft comprising a spar forming the forward portion of said blade structure and a collapsible rear blade structure connected to said spar and spaced rearwardly therefrom to form the rearward portion of said blade structure when in an extended position, said rear blade structure being connected to said spar in a manner permitting said rear blade structure to be collapsed inwardly toward said spar to present an overall profile together with said spar of relatively low air drag and with substantially no lift capabilities, a skin connected between said space and said rear blade structure and forming an exterior covering therebetween and providing therewith a lift profile when in an extended position and being folded between said spar and said rear blade structure in a collapsed position, said rear blade structure including a plurality of ribs pivotally connected at their inner ends to said spar.

3. A blade structure for rotary wing aircraft comprising a spar forming the forward portion of said blade structure and a collapsible rear blade structure connected to said spar and spaced rearwardly therefrom to form the rearward portion of said blade structure when in an extended position, said rear blade structure .being connected to said spar in a manner permitting said rear blade structure to be collapsed inwardly toward said spar to present an overall profile together with said spar of relatively low air drag and with substantially no lift capabilities, a skin connected between said space and said rear blade structure and forming an exterior covering therebetween and providing therewith a lift profile when in an extended position and being folded between said spar and said rear blade structure in a collapsed position, said rear blade structure including a plurality of ribs pivotally connected at their inner ends to said spar, and a trailing bar member of substantially the same longitudinal dimension as said spar, said ribs each being pivotally connected to said'bar member and said bar member being displaceable longitudinally and inwardly toward said spar for collapsing said ribs inwardly toward said spar.

4. A blade structure for a convertible rotary wing aircraft comprising a longitudinally elongated spar forming the forward portion of said blade structure, a longitudinally elongated bar member and a plurality of ribs extending between said spar and said bar member and being pivotally connected adjacent their inner ends to said spar and pivotally connected adjacent their outer ends to said bar member, flexible material covering said wing structure at least between said spar and said bar member and of a length to permit said ribs to be fully extended between said spar and said bar member for forming an overall blade profile having lift capabilities, said ribs being pivotal upon relative longitudinal and-inward movement of said spar and said bar members to permit said bar member to be moved adjacent said spar to provide a profile of low lift capabilities, the covering being foldable between said spar and bar member to permit said movement.

5. A blade structure for a convertible rotary wing aircraft comprising a longitudinally elongated spar forming the forward portion of said blade structure, a longitudinally elongated bar member and a plurality of ribs extending between said spar and said bar member and each being pivotally connected adjacent its one end to said spar and pivotally connected adjacent its opposite end to said bar member, flexible material covering said wing structure at least between said spar and said bar member and of a length to permit said ribs to be fully extended between said spar and said trailing bar member for forming an overall blade profile having lift capabilities, said ribs being pivotal upon relative longitudinal movement of said spar and said bar members to permit said bar member to be moved adjacent said spar to provide a profile of low lift capabilities, the covering being foldable between said spar and said bar member to permit said movement, said covering being connected at each of its ends to said spar and extending around said trailing bar member and being secured thereto.

6. A blade structure for a convertible rotary wing aircraft'comprising a longitudinally elongated spar forming the forward portion of said blade structure, a longitudinally elongated bar member and a plurality of ribs extending between said spar and said bar member each being pivotally connected adjacent its one end to said spar and pivotally connected adjacent its opposite end to said bar member, flexible material covering said wing structure at least between said spar and said bar member and of a length to permit said ribs to be fully extended between said spar and said trailing bar member for forming an overall blade profile, said ribs being pivotal upon relative longitudinal movement of said spar and said bar members to permit said bar member to be moved toward said spar, the covering being foldable to permit said movement, said ribs including portions adjacent said spar which may be moved together, and means defined between said spar and said ribs for moving said rib portions together when said ribs are pivoted inwardly adjacent said spar.

7. A blade structure for a convertible rotary wing aircraft comprising a longitudinally elongated spar forming the forward portion of said blade structure, a longitudinally elongated bar member and a plurality of ribs extending between said spar and said bar member each being pivotally connected adjacent its one end to said spar and pivotally connected adjacent its opposite end to said trailing bar member, flexible material covering said wing structure at least between said spar and said bar member and of a length to permit said ribs to be fully extended between said spar and said trailing bar member for forming an overall blade profile, said ribs being pivotal upon relative longitudinal movement of said spar and said bar members to permit said bar member to be moved toward said spar,

the covering being foldable to permit said movement, said ribs including portions-adjacent said spar which may be moved together, means defined between said spar and said ribs for moving said rib portions together when said ribs are pivoted inwardly adjacent said spar, and spring means biasing said movable portions of said ribs outwardly.

8. A blade structure for a convertible rotary wing aircraft comprising a longitudinally elongated spar forming the forward portion of said blade structure, a longitudinally elongated bar member and a plurality of ribs extending between said spar and said bar member, each being pivotally connected adjacent its one end to said spar and pivotally connected adjacent its opposite end to said trailing bar member, flexible material covering said wing structure at least between said spar and said bar member and of a length to permit said ribs to be fully extended between said spar and said trailing bar member for forming an overall blade profile having lift capabilities, said ribs being pivotal upon relative longitudinal movement of said spar and said bar members to permit said bar member to be moved adjacent said spar to form a profile having low lift capabilities, the covering being foldable between said spar and said bar member to permit said movement, each of said ribs comprising a substantially U-shaped element having a top rib portion and a bottom rib portion connected by a web portion, said web portion being pivotally connected to said bar member, said leg portions diverging outwardly from said web portions into engagement with said covering.

9. A blade structure for a convertible rotary wing aircraft comprising a longitudinally elongated spar forming the forward portion of said blade structure, a longitudinally elongated bar member and a plurality of ribs extending between said spar and said bar member, each being pivotally connected adjacent its one end to said spar and pivotally connected adjacent its opposite end to said trailing bar member, flexible material covering said wing structure at least between said spar and said bar member and of a length to permit said ribs to be fully extended between said spar and said trailing bar member for forming an overall blade profile, said ribs being pivotal upon relative longitudinal movement of said spar and said bar members to permit said bar member to be moved toward said spar, the covering being fold- .able to permit said movement, each of said ribs comprising a substantially U-shaped element having a top rib portion and a bottom rib portion connected by a web portion, said web portion being pivotally connected to said bar member, said leg portions diverging outwardly from said web portions into engagement with said covering, said rib structure including wedge-shaped ends on each leg, said spar having a recess with inwardly converging walls forming complementary wedge-shaped engaging surfaces with the ends'of said rib members, said rib members being pivotally mounted such that when they are pivoted inwardly toward said spar said leg portions of said ribs are moved together.

10. A blade structure for a convertible rotary wing air craft comprising a longitudinally elongated spar forming the forward portion of said blade structure, a longitudinally'elongated bar member and a plurality of ribs extending between said'spar and said trailing bar member, each being pivotally connected adjacent its one end to said spar and pivotally connected adjacent its opposite end to said trailing bar member, flexible material covering said wing structure at least between said spar and said bar member and of a length to permit said ribs to be fully extended between said spar and said trailing bar member for forming an overall blade profile having lift capabilities, said ribs being pivotal upon relative longitudinal movement of said spar and said bar members to permit said bar member to be moved adjacent said spar to form a profile of low lift capabilities, the covering being foldable between said spar and said bar member to permit said movement, said trailing bar portion comprising a flap having a pointed end for defining the profile of the trailing edge of said blade structure.

11. A blade structure for a convertible rotary wing aircraft comprising a longitudinally elongated spar forming the forward portion of said blade structure, a longitudinally elongated bar member and a plurality of ribs extending between said spar and said trailing bar member, each being pivotally connected adjacent its one end to said spar and pivotally connected adjacent its opposite end to said trailing bar member, flexible material covering said wing structure at least between said spar and said bar member and of a length to permit said ribs to be fully extended between said spar and said trailing bar member for forming an overall blade profile having lift capabilities, said ribs being pivotal upon relative longitudinal movement of said spar and said bar members to permit said bar member to be moved-adjacent said spar to form a profile of low lift capabilities, the covering being foldable between said spar and said bar member to permit said movement, and means connected to said bar member for shifting sa'id bar member in a direction substantially parallel to the longitudinal axis of said -spar and inwardly in respect thereto for folding said rear blade structure behind said forward blade structure and in a reverse manner for forming a lift producing overall blade profile.

12. A blade structure for a convertible rotary wing aircraft comprising a longitudinally elongated spar forming the forward portion of said blade structure, a longitudinally elongated bar member and a plurality of ribs extending between said spar and said trailing bar member each being pivotally connected adjacent its one end to said spar and pivotally connected adjacent its opposite end to said trailing bar member, flexible material covering said wing structure at least between said spar and said bar member and of a length to permit said ribs to be fully extended between said spar and said trailing bar member for forming an overall blade profile having lift capabilities, said ribs being pivotal upon relative longitudinal movement of said spar and said bar members to permit said bar member to be moved adjacent said spar to form a profile of low lift capabilities, the covering being foldable between said spar and said bar member to permit said movement, and means connected to said bar member for shifting said bar member in a direction substantially parallel to the longitudinal axis of said spar and inwardly in respect thereto for folding said rear blade structure behind said forward blade structure and in a reverse manner for forming a lift producing overall blade profile, said bar being of a Weight such that during rotation of said blade structure it is urged outwardly from said spar to hold said rear blade structure in an erected air lift producing profile.

13. A blade structure for a convertible rotary wing aircraft comprising a longitudinally elongated spar forming the forward portion of said blade structure, a longitudinally elongated bar member and a plurality of ribs extending between said spar and said trailing bar member each being pivotally connected adjacent its one end to said spar and pivotally connected adjacent its opposite end to said trailing bar member, flexible material covering said wing structure at least between said spar and said bar member and of a length to permit said ribs to be fully extended between said spar and said trailing bar member for forming an overall blade profile having lift capabilities, said ribs being pivotal upon relative longitudinal movement of said spar and said bar members to permit said bar member to be moved adjacent said spar to form a profile of low lift capabilities, the covering being foldable between said spar and said bar member to permit said movement, means for mounting said spar on a rotor head, and means connectable to said bar member to move said bar member with said ribs and said covering inwardly toward said spar.

14. A blade structure, according to claim 12, wherein said means for moving said trailing bar member comprises a rotatable crank rotatably mounted on said spar and means connected to said crank for rotating said crank for shifting said bar member between an erected position in spaced relationship to said spar with said rib members extending substantially perpendicular to the longitudinal axis thereof and to a forward position in which the rib members extend substantially parallel to the axis of said spar with the trailing bar member moved closer into said spar.

15. A blade structure, according to claim 12, wherein said means to move said trailing bar member includes a three-armed lever member, said three-armed lever member having one arm pivotally mounted on said spar and another arm pivotally connected to said trailing bar member, said three-armed lever having a third arm, and control means connected to said third arm of said threearmed lever for shifting said lever about the pivotal connection of said first arm for erecting and collapsing said rear blade structure.

16. A blade structure, according to claim 12, including a rotor, means mounting pivotally said sparon said rotor, a plate member mounted concentrically in respect to said rotor and being rotatable, a control arm carried by said plate member and connected to the trailing bar member of said blade, and means to rotate'said plate member to shift said control arm and said trailing bar member for erecting and collapsing said rear blade structure.

17. A blade structure, according to claim 12, wherein said means for moving said trailing bar member comprises a rotatable crank rotatably mounted on said spar and means connected to said crank for rotating said crank for shifting said bar to a location in spaced relationship to said spar with said rib members extending substantially perpendicular to the longitudinal axis thereof and to a forward position in which the rib members extend substantially parallel to the axis of said spar with the trailing bar member moved closer into said spar, a rod member pivotally connected to said trailing bar member, a tilting right angle lever member pivotally connected on its one end to said rod member and a reciprocating rod member adapted to move upwardly and downwardly to contact said tilting arm member for pivoting said arm member for shifting said rod member.

18. A helicopter rotor comprising a rotor at least one blade structure carried on said rotor extending outwardly therefrom and having a forward spar forming the forward portion of said blade structure and means including a collapsible covering defining the rear portion of said blade structure, said blade structure defining a lift profile when extended and a profile of substantially no lift when collapsed, and control means mounted on said rotor and connected to said collapsible rear structure for positioning said rear structure outwardly in an erected position in respect to said spa-r and for moving said rear structure to a collapsed position adjacent said spar.

19. A helicopter rotor comprising a rotor head at least one blade carried on said rotor head extending outwardly therefrom and having a forward spar forming the forward portion of said blade structure and means including a collapsible covering defining the rear portion on said blade structure, said blade structure defining a lift profile when extended and a profile of substantially no lift when collapsed, and control means mounted on said rotor head and connected to said collapsible rear structure for positioning said rear structure outwardly in an extended position in respect to said spar and for moving said rear structure to a collapsed position adjacent said spar, including a fluid control cylinder and a rod member slidable in said cylinder under the influence of fluid pressure in said cylin-' der for varying the position of said rear blade structure.

20. A blade structure for a convertible rotary wing aircraft comprising a longitudinally elongated spar forming the forward portion of said blade structure, a longitudinally elongated bar member and a plurality of ribs extending between said spar and said bar member each being pivotally connected adjacent its one end. to said spar and pivotally connected adjacent its opposite end to said trailing bar member, flexible material covering said wing structure at least between said spar and said bar member and of a length to permit said ribs to be fully extended between said spar and said trailing bar member for forming an overall blade profile, said ribs being pivotal upon relative longitudinal movement of said spar and i said bar members to permit said bar member to be moved (toward said spar, the covering being foldable to permit said movement, said blade structure defining a lift profile when extended and a profile of substantially no lift when collapsed, including means connected to said bar member for displacing said bar member with said ribs toward said spar to a collapsed position, said means including a reciproca'ble push rod member, said push rod member being vertically reciprocable, a swivel joint pin, means mounting the inner end of said spar on said joint pin for pivotal movement about the same axis as said swivel joint pm, a tipping lever connected to said connecting rod and coupled to said push rod and being movable by movement of said push rod to move said connecting bar rod and'said trailing bar member, said tipping lever being provided with an arcuate link for engaging said push rod.

References Cited by the Examiner UNITED STATES PATENTS 2,074,807 -3/ 1937 Reed l70160.1

FOREIGN PATENTS Ad. 29,510 5/ 1925 France. Ad. 3 0,075 10/ 1925 France.

612,675 5/ 1935 Germany. 509,244 7/ 1939 Great Britain.

SAMUEL LEVINE, Primary Examiner. E. A. POWELL, JR., Assistant Examiner. 

18. A HELICOPTER ROTOR COMPRISING A ROTOR AT LEAST ONE BLADE STRUCTURE CARRIED ON SAID ROTOR EXTENDING OUTWARDLY THEREFROM AND HAVING A FORWARD SPAR FORMING THE FORWARD PORTION OF SAID BLADE STRUCTURE AND MEANS INCLUDING A COLLAPSIBLE COVERING DEFINING THE REAR PORTION OF SAID BLADE STRUCTURE, SAID BLADE STRUCTURE DEFINING A LIFT PROFILE WHEN EXTENDED AND A PROFILE OF SUBSTANTIALLY NO LIFT WHEN COLLAPSED, AND CONTROL MEANS MOUNTED ON SAID ROTOR AND CONNECTED TO SAID COLLAPSIBLE REAR STRUCTURE FOR POSITIONING SAID REAR STRUCTURE OUTWARDLY IN AN ERECTED POSITION IN RESPECT TO SAID SPAR AND FOR MOVING SAID REAR STRUCTURE TO A COLLAPSED POSITION ADJACENT SAID SPAR. 